It is known to apply focused beams of electromagnetic radiation to investigate samples using ellipsometers, polarimeters, reflectometers and spectrophotometers. Numerous Patents describe this, such as:    U.S. Pat. No. 7,522,279 to Liphardt et al.;    U.S. Pat. No. 7,518,725 to Liphardt et al.;    U.S. Pat. No. 7,057,717 to Liphardt et al.;    U.S. Pat. No. 7,075,649 to Johs et al.;    U.S. Pat. No. 6,950,182 to Liphardt et al.;    U.S. Pat. No. 7,489,400 to He et al.;    U.S. Pat. No. 7,317,530 to Liphardt et al.;    U.S. Pat. No. 7,468,794 to Liphardt et al.;    U.S. Pat. No. 7,075,650 to Johs et al.;    U.S. Pat. No. 7,385,698 to Welch et al.;    U.S. Pat. No. 7,385,697 to Woollam et al.;    U.S. Pat. No. 7,345,762 to Liphardt et al.;    U.S. Pat. No. 6,804,004 to Johs et al.;    U.S. Pat. No. 7,336,361 to Liphardt et al.;
The forgoing Patents are all incorporated by reference into the specification.
In addition, a computer search for Patents having words “conjugate ratio” and “ellipsometer” or “ellipsometery” provided U.S. Pat. Nos. 6,583,877; 6,485,703; 6,323,946; 5,955,377; 5,917,594; 5,869,272; 5,639,671; 5,631,171; 5,629,214; 5,552,272; 5,550,063; 5,541,057; 5,494,829; 5,494,801; 5,482,830; 5,468,606; 5,418,136.
To avoid confusion and because it is the basis of the present invention, it is specifically noted at this point that, while the present invention system has certain similarities to lens systems which magnify an image at a screen, the present invention is not applied as magnifying, (ie. zoom), lens system. In particular, a magnifying lens system is applied to a scenario in which the screen (eg. a camera screen), and the imaged subject viewed at said screen remain at the same locations as the image at the screen is magnified. The present invention is not concerned with magnification, and instead for a set conjugate ratio, adjusts the configuration of lens elements to image a substantially point source of electromagnetic radiation onto a screen or sample in a manner which minimizes the effects of aberration. Thus, a substantially optimally focused spot size is achieved.
Even in view of the prior art, need remains for new lens configurations which are suitable for application in sample investigating systems, to enable flexibility in providing focused beams at samples where the effects of aberration are minimized. In particular, a lens system which would allow, for any set “conjugate ratio”, ie.:
      the  distance  from  a  source  to  said  lens  system        the  distance  from  said  lens  system  to  said  sample  reducing the effects of aberration of beam focus on the sample, without physically moving a source; sample or detector.
Finally, for general interest, it is noted that the “object distance” is the distance from a source to lens, the “image distance” is the distance from said lens system to a sample such that the equation:
            1              object  distance              +          1              image  distance              =      1          focal  length      is satisfied, for paraxial beams.